The ability of a camera to produce a photograph that faithfully depicts a scene is governed in large part by its optical performance. There are several technical variables that can be used to evaluate optical performance based on the quality of the photograph or picture. For instance, there are systems that can measure the sharpness of the photograph. Sharpness is also monitored during an autofocus process in which sharpness values are calculated over a number of image captures, as the distance between a camera lens and the plane of an image sensor is changed or “swept”. This may be referred to as sharpness sweep data. The autofocus process attempts to find the optimum location of the lens (e.g., its distance to the sensor) that yields the sharpest captured image. The actual sharpness capability of a camera typically varies in different parts of the image sensor array, due to the imperfect physical characteristics of the lens. For instance, the center of a captured image is typically sharper than the corner areas. Another optical characteristic that is often evaluated is distortion, that is whether a geometric shape in an image has been distorted (e.g., where a straight line becomes curved). Distortion may also be position dependent over the sensor area of the image sensor.
Several measurements of the optical characteristics of a camera component such as a lens are often performed during manufacture testing, to ensure that the specimens released to the end user are within a given performance specification. One characteristic that is tested is that of optical tilt. See FIG. 2 in which a portion of an ideal camera is depicted where the lens and sensor have no relative optical tilt, while FIG. 1 shows (in a rather exaggerated way) the presence of a small amount of tilt, where the lateral lens axis shown is not parallel to the lateral sensor axis. The latter leads to malformation of the optical image of the scene on the sensor array, which may result in a certain amount of blur or defocus in the captured image. Techniques for measuring the optical tilt, and then using it to judge whether or not a lens or camera module is a satisfactory specimen, are available and can be used during high volume manufacture testing of camera modules and camera lenses by themselves. Such techniques, however, are quite complex. In addition to alignment with a test target pattern, high precision mechanical components including a laser light source and mirrors, together with the needed automatic test equipment, are required. For low volume manufacturing of larger lenses such as those used in professional digital SLR cameras, such techniques may be adequate. However, they may not be suitable for high volume manufacturing of camera modules and lenses that are used in small, low cost, consumer electronic, multi-function mobile devices, such as smart phones and tablet computers. The lenses used in such devices are relatively small and the resulting photographs that are taken may be more susceptible to variations in optical characteristics. In addition, high volume manufacture testing of such devices may create a large expense when using the conventional testing techniques, due to the sheer volume of lenses and camera modules that need to be tested.